The present invention generally relates to a coil and more particularly, to a chip coil of a wire wound type having a high magnetic shielding property and which may be manufactured with superior productivity. The invention also relates to a method of manufacturing such a chip coil.
Recently, as electronic appliances are increasingly being made in a thin and compact size, it has been a requirement to mount or load electronic components and parts onto an electronic appliance with a high density. Coils are not an exception with respect to such a requirement, and it has become necessary to form coils into chips and also to provide them with a magnetic shielding property, which is indispensable to the high density mounting.
A conventional chip coil provided with the magnetic shielding property is known to the art, having a construction as shown in FIG. 6. In FIG. 6, the known chip coil includes a bobbin B made of ferrite or the like and formed with flange portions Fa and Fb formed at opposite ends thereof, and a wire (not shown) wound around a barrel portion of said bobbin B. Over the wound wire referred to above, a layer R of resin mixed with magnetic particles, hereinafter "magnetic particle-containing resin," is formed, by coating the magnetic particle-containing resin in a liquid form onto the wire through employment of a dispenser or the like for subsequent curing or hardening. At the opposed end portions of the flange portion Fa of the bobbin B, there are respectively formed electrodes Ea and Eb, and one end of the wire wound around the barrel portion of the bobbin B is connected to the electrode Ea, while the other end thereof is connected to the electrode Eb.
In FIG. 7, there is shown another example of a conventional chip coil provided with a magnetic shielding property, with like parts in FIG. 6 being designated by like reference symbols. The known chip coil of FIG. 7 also includes a bobbin B, flange portions Fa and Fb formed at opposite ends of the bobbin B, and a wire W wound around the barrel portion of the bobbin B. Below the flange portion Fa, there are provided lead electrodes La and Lb, with one end of the wire W being electrically connected to the lead electrode La, and the other end thereof to the electrode Lb respectively. Over the bobbin B having the flange portions Fa and Fb and wound with the wire W, there is provided a covering layer RB of magnetic particle-containing resin formed by molding the resin with a metallic mold, with one end of each of the lead electrodes La and Lb being exposed externally.
However, the conventional chip coils described above have problems as follows.
Specifically, in the conventional chip coil as shown in FIG. 6, since the magnetic particle mixed resin in the liquid form must be coated through employment of a dispenser, etc., it is necessary to reduce the viscosity of the magnetic particle mixed resin in the liquid form by lowering the mixing ratio of the magnetic particles, and thus, there has been the disadvantage that the covering layer RB formed by curing such magnetic particle-containing resin is inferior in the magnetic shielding property. Moreover, if there is any scattering (variation) in the amount of coating by the magnetic particle-containing resin in the liquid form, this will result in the variation of the inductance and the quality factor Q in the final products. Furthermore, since complicated procedures are required for the coating of the magnetic particle-containing liquid form resin through employment of a dispenser or the like, and since a considerable time is taken to form the layer R by curing said resin, there is the disadvantage that the resultant chip coils tend to be high in cost and poor in productivity.
On the other hand, in the conventional chip coil as shown in FIG. 7, there are also the disadvantages that when the mixing ratio of the magnetic particles in the magnetic particle-containing liquid form resin is lowered, the magnetic shielding property of the layer RB undesirably becomes insufficient. On the other hand, if the mixing ratio thereof is made high, the viscosity of the resin becomes large, which also results in inconveniences, for example, the workability of the resin for molding of the covering layer RB by the metallic mold may be impaired or such molding may not be able to be effected in certain cases. Additionally, severe abrasion of the metallic mold by the magnetic particles tends to give rise to an increase in the production cost.